Magnetic circuit means and alloy components of constant magnetic permeability therefor



Feb. 16, 1965 K. BUNGARDT EI'AL 3,170,112

- MAGNETIC CIRCUIT MEANS AND ALLOY COMPONENTS OF CONSTANT MAGNETIC PERMEABILITY THEREFOR Filed Feb. 15, 1960 2 Sheets-Sheet 1 Fig.1

V/ua r Fig.2

Jnvem'ors F 1 1965 K. BUNGARDT ETAL 3,170,112 7 MAGNETIC ,CIRCUIT MEANS AND ALLOY COMPONENTS OF CONSTANT MAGNETIC PERMEABILITY THEREFOR Filed Feb. 15, 1960 2 Sheets-Sheet 2 44/4 ldfilvE NTO R S ATTORNEYS.

United States Patent 3,170,112 MAGNETIC CmCUIT MEANS AND ALLOY COM- PONENTS OF CONSTANT MAGNETICPERI VIEA- BILITY THEREFOR 1 Karl Bungardt and Hermann Dietrich, Krefeld, Germany,

assignor's to Deutsche Edelstahlwerire schaft, Krefeld, Germany 'Filed Feb. 15, 1960, Ser. N 8,731 Claims priority, application Germany, Feb. 21, 1959, .D30,051 :2 Claims. (Cl. 324-34) The present invention relates to means wherein at least one alloy component forms part of a magnetic circuit and becomes heated'during functioning of'said means, e.g., where such a component co-operates with a magnetic monitoring means responsive to changes inform or movement of the said component or ai'pa rt .with.iwhich it is associated, and the invention is essentially concerned with alloy, at the expense of its content of iron, and without changing its content of other constituents, a quantity of' 5 and 35%, preferably between .20 and Aktiengesell sible resistivity, and which nevertheless retain the desired alloys for the production of'such components-which shall have a magnetic permeability thatdoes notichange up to temperatures of at least 500 C. Components as afores'aid 'are required'for instance in' the determination of relative changes in length, eccentricities, and the like of v shafts or other rotating parts in machines for example, steam or gas turbines, internal combustion engines, and

so forth. In recent years the performance of such measj Iur'ements has become a matter of increasing importance i in the operational control of turbines. The ,measure-'' ments are based upon thedetermination of certainma'g netic properties, of materials built intothemachines which it is desired to monitor.' Consequently, the performance of such measurements depends'upon the availability of a material which does not lose itsmagnetic properties at the elevated. temperatures at which the measurements A must be performed, and which at these temperature levels v is non-scaling, heat resistant, as wellas corrosion-resistant.

In known methods of performing such measurements which have in the past been restricted t the low tempera- Y ture range, not exceeding' approximately 200 C., the. 'material employed for the'purpose in question has been.

an iron-nickel alloy containing 36% nickel. However,

since the Curie point of this alloy is located at approximately 250C. it cannot be used for measurements at more elevated temperatures. Moreover, this alloy is also unsuitable for use at higher temperatures because it tends to form scale.

Unexpectedly it has now been found that an iron:

chrome alloy containing about 520%, preferably 7-15 chromium 0.5 to 10%, preferably 1 7%, aluminium, 0.2

to 3%, preferably 0.5 to 2%, silicon, up to 0.2% carbon, remainder iron, with the usual impurities of manganese, sulphur, and phosphorus which arise in the melting process, is outstandingly suitable for application to the purpose in view. The alloy has a magnetic permeability of about 200 gauss/oersted and this remains substantially constantice Patented Feb. 16, 1965 With a view to further extending the temperature range of constant permeability itis also proposed to add to the favourable'magnetic properties This is a specially de sirable result for the application of such alloys to' the purposes taken in view because their resistivityreduces the generationof eddy currents.

The accompanying graphs FIGS; land-2 schematically illustrate the permeability change as'a function of temperature and of the field strength; FIG'; '3""illustrates one way in which the alloy-component attached to 'a shaft,

location of this point the approximately 500 C, temperature level is shown at t co-operates with magnetic monitoring means. FIGS. 4

and 4a diagrammatically illustrate part of a. turbine equipped with the alloy component and co-operative monitoring means and FIG. 5 shows another modification,

1 1 FIG..1 representsthe. relationship-between permeability and temperature of an alloy constitutedas proposed by the present invention. ,It will be seen that this interdependence isapproximately linear up to a point: indicated by t In order to give'a rough idea of theactual FIG.-2 schematically represents permeability. .as a function of-field strength H. At a point markedH in the plot the field strength is about .100 moe.. Thegraph further shows that the three illustrated'curves practically coincide at 'field strengths below this point. The curves diverge slightly when H is exceeded. The deviation from the desired linear relationship generally increases with in- I is a curve plotted at atemperacreasing temperature. I ture of 20 0., whereas curve 11 is for 350 0., and curve "IIIfor -500 C v FIG. 3 showsa shaft 1 running in bearings 2. ex-

a disc 4.

tension 3 of reduced-diameter of the'sha-ftcarries This disc is offan alloy consisting of:

. Percent Chromium 12.50 Aluminium 1.00 Silicon 0.95 Carbon 0.17

The remainder iron with the usual impurities of mangav nese, sulphur and phosphorus which arise in the melting within the temperature range between 0 and 500 C. and

it can besuccessfully used at temperatures above 250 C. Nor does this value change when the field strength increases, atyleast below 100 moe. Owing to its content of aluminium and silicon the proposed alloy forms no scale at the temperatures in question; As a result of 'creep resistance of the alloy partor all of the aluminium may be replaced by corresponding quantities of molybdenum and/or tungsten. This substitution does notatfectthe characteristic magnetic properties of the'alloy.

of hot and cold deform As will be readily understood from thefigure, the disc revolves with the shaft and therefore participates in every oscillation or other movement performed bythe shaft." At 5, fiand 7 are magnet cores schematically shownas of horseshoe shape. In each case a magnetic flux (alternating field) is generated by a coil, not shown. The magnetic circuits areclosed through disc 4 across the air gaps 8, 9 and 10. The inductance of the magnet cores,

which function as transmitters, changes when the widths e of gaps 8, 9 and lochange. This means that the changes in the inductance of the cores reflect oscillations for example, of the revolving shaft '1. Since the shaft, which may be the shaft of a turbine, runs in a steam atmosphere having'a temperature of about 500 C. the material of disc 4'is likewise exposed to this temperature and to the. J corrosive attack occasioned thereby, but the discmade of U on its revolving components 11 carries the rings 12 and.

13 which are of the aforesaid alloy. These rings are secured by screws l dwhich engage the revolving components 11.

In FIG. 5, two. shafts are shown flanged together at 15. The flange itself is used to hold a disc 16 by screw clamping'means 17, the disc being of the aforesaid alloy.

The rings or discs referred to magnetically serve as armatures of magnetic circuits.

By means of the invention the running of a turbine for example maybe magnetically monitored continuously, a precaution which is especially necessary or desirable in modern high-speed and high-power turbines. .The magnetic monitoring means may be associated with externally visual indicating means, but the magnetic means and the associated means form per se no part of the present in vention and need be no further illustrated and may be of conventional pattern, the essence of this invention residing in the material of which the key component, whether it be a disc, ring or the like as specifically mentioned or other normal part of the machine, is produced.

Examples of other suitable alloys that will serve are:

, Percent Chromium Q. 12.00 Molybdenum 2.00 Silicon 1.00 Carbon 0.15 the rest being iron with impurities as aforesaid Percent Chromium 13.00 Tungsten 3.00 Silicon 0.80 Carbon 0.12

the rest being iron with impurities as aforesaid.

Percent Chromium 12.50 luminium 1.05 Silicon 0.95 Carbon 0.02 Cobalt 22.00

the rest being iron with impurities as aforesaid.

What we claim is:

1. In a machine incorporating at least one component carried by a rotatable part of the said machine which becomes heated in the functioning of the machine and magnetic monitoring means co-operating with said component and responsive to changes in form or movement which take place in said part during its rotation, the improvement which consists in that the said component comprises an iron-chromium alloy consisting essentially of 5.0 to 20.0% chromium, 0.5 to 10.0% of aluminum, 0.2 to 3.0% silicon, 0 to 35% cobalt, up to 0.2% carbon, and the remainder iron, the said component having a permeability which remains constant up to a temperature of at least 500 C. and at field strengths up to at least- 100 moe. and which is non-scale-forming at said temperatures. i a

2. In a machine incorporating at least one component carried by a rotatable part of the said machine which becomes heated in the functioning of the machine and magnetic monitoring means co-operating with said component I and responsive to changes in form or movement which take place in said part during its rotation, the improvement which consists in thatthe said component comprises an iron-chromium alloy consisting essentially of 5.0 to 20.0% chromium, 0.5 to 10% in total of at least oneof the elements selected from the group consisting of aluminum, molybdenum'and tungsten, 0.2 to 3.0% silicon, 0 to 35% cobalt, up to 0.2% carbon, and the remainder iron, the said component having a permeability which remains constant up to a temperature of at least 500 C. and at field strength up to at least 100 moe. and which is non-sc'ale-forming at said temperatures.

References Cited by the Examiner UNITED STATES PATENTS 1,338,134 4/20 Honda.

1,763,421 6/30 De Vries.

2,864,997 12/58 Von Basel 32434 2,932,568 4/60 Kt gerise et al. i 126 X LLOYD MCCOLLUM, SAMUEL BERNSTEIN,

- Examiners. 

2. IN A MACHINE INCORPORATING AT LEAST ONE COMPONENT CARRIED BY A ROTATABLE PART OF THE SAID MACHINE WHICH BECOMES HEATED IN THE FUNCTIONING OF THE MACHINE AND MAGNETIC MONITORING MEANS CO-OPERATING WITH SAID COMPONENT AND RESPONSIVE TO CHANGES IN FORM OR MOVEMENT WHICH TAKE PLACE IN SAID PART DURING ITS ROTATION, THE IMPROVEMENT WHICH CONSISTS IN THAT THE SAID COMPONENT COMPRISES AN IRON-CHROMIUM ALLOY CONSISTING ESSENTIALLY OF 5.0 TO 20.0% CHROMIUM, 0.5 TO 10% IN TOTAL OF AT LEAST ONE OF THE ELEMENTS SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, MOLYBDENUM AND TUNGESTEN, 0.2 TO 3.0% SILICON, 0 TO 35% COBALT; UP TO 0.2% CARBON, AND THE REMAINDER IRON, THE SAID COMPONENT HAVING A PERMEABILITY WHICH REMAINS CONSTANT UP TO A TEMPERATURE OF AT LEAST 500*C. AND AT FIELD STRENGTH UP TO AT LEAST 100 MOE. AND WHICH IS NON-SCALE-FORMING AT SAID TEMPERATURES. 